The present invention relates to a pressure limiting valve and related method for testing the operability of a backflow preventer. More specifically, the present invention relates to a pressure limiting valve with opposing springs that limits the pressure of fluid deliverable to a low pressure gauge in applications for testing the operability of a backflow preventer having one or more check or relief valves located on high or low pressure systems.
For decades, there have been local, state and federal health and safety regulations requiring the installation of valves known as backflow prevention devices on potable and non-potable water systems. The purpose of the backflow prevention device is to protect the main water distribution system from contamination or pollution that may originate from liquid backflow from lines attached to the distribution system as a result of very low or negative pressures. Normally, liquid in a water supply system is maintained at a significant pressure to enable water to flow from the source to a tap (e.g., a faucet), shower, etc. When the pressure in the connecting pipes falls significantly or becomes negative (i.e., reverses), contaminated water from the ground or other storage sources may be drawn into or back through the pipe toward the distribution center. Pressurized water distribution systems known in the art have been known to experience such significant pressure reductions or pressure reversals as a result of water main bursts, freezing pipes or an unexpectedly high demand on the water system, such as can be common when fighting large wild fires in urban areas of Southern California. The backflow prevention devices are designed to prevent contamination of the potable water system. Typically, backflow prevention devices required by law must be installed in accordance with plumbing and/or building codes and must be tested for operation each year.
Typical backflow prevention devices will make use of either an air gap or a mechanical backflow prevention assembly, such as a check valve, between the water delivery point (e.g., the faucet or shower) and the mains water or local water supply. In the United States, the Environmental Protection Agency (“EPA”) regulates the contaminants and the associated maximum containment level (MCLS) of local drinking supplies. For example, the National Primary Drinking Water Regulations (NPDWRs or Primary Standards) are enforceable regulatory standards that apply to public water systems. Primary Standards protect public health by limiting the levels of contaminants in drinking water. As a result, in order to maintain levels of contaminants that conform to the Primary Standards, the viability of the backflow prevention device must be tested (typically annually). For a system that includes a check valve, for example, the backflow prevention device may include a series of test cocks and shut-off valves that need annual testing.
The Cross-Connection Control Manual, the contents of which are herein incorporated by reference in their entirety, was first printed nearly forty years ago and is part of a safety program that provides guidelines for products, product performance, installations, training and testing of backflow prevention devices. Environmental Protection Agency, Office of Water, Cross-Connection Control Manual (1973, Reprinted in 2003 with Technical Corrections). Related laws and regulations, standard underwriters and the EPA, which publishes the Cross-Connection Control Manual, require certain backflow safeguards discussed in detail in the Cross-Connection Control Manual. These regulations and guidelines are designed to protect public health from unsafe drinking water from backflow in unprotected water systems or from backflow in cross-connections of potable water lines with non-potable water lines. As such, backflow prevention devices are typically required to be installed along some portion of the piping system to prevent unwanted contamination from entering the system due to a low or reverse pressure environment. As such, to ensure the backflow prevention devices are operating properly and efficiently (at least to within predefined specifications), the Cross-Connection Control Manual calls for the use of backflow prevention devices that have some method of being tested. Testing ensures that the devices perform at predetermined performance specifications under hydraulic conditions. For example, testing would reveal that a simple check valve is not reliable to hold drip-tight over time. Thus, there has been a need for more sophisticated valves that hold tighter seals for longer durations in preventing reverse flow in distribution systems.
In general, the Cross-Connection Control Manual categorizes most backflow prevention devices into four basic configurations that include: (1) Double Check Valve Assemblies, also known as (“DC”) assemblies; (2) Reduced Pressure Principle Assemblies, also known as (“RP”) assemblies; (3) Pressure Vacuum Breaker Assemblies (“PVB”); and (4) Spill Resistant Pressure Vacuum Breaker Assemblies (“SVB”).
A double check valve assembly (DC) essentially includes two single check valves coupled in series within one body. The body typically includes a series of test cocks and a pair of shut-off valves at each end of the assembly. The test cocks provide the ability to determine whether either or both of the check valves are operating within predefined pressure ranges, or completely inoperative altogether (unable to hold a positive back pressure). Each check valve is spring loaded such that some predetermined amount of pressure must exist (e.g., one pound or more) to open the valves. Double check valve combinations of this nature are typically used to protect against low to medium hazard conditions and may be used under continuous pressure to protect against both back-siphonage and backpressure conditions.
A reduced pressure principle assembly backflow preventer is essentially a modified double check valve assembly. In this respect, the (RP) assembly includes two check valves, as mentioned above, with a relief vent valve placed therebetween. The pressure of the liquid disposed between the two check valves is preferably kept at a pressure of at least five pounds less than the pressure of the incoming supply. In the event the pressure between the two check valves decreases beyond a predetermined threshold (e.g., the aforementioned five pounds), the relief valve opens to allow air into the backflow device stopping back-siphonage between the two check valves when the pressure drops to about approximately two PSI. As such, the (RP) assembly typically provides better protection from back-siphonage and low pressure conditions than the (DC) assembly described above. The (RP) assembly can protect against back-siphonage and low pressure when both the first and second check valves become fouled. Additionally, this device can be used under constant pressure and at high hazard installations. Of course, each device includes test cocks and shut-off valves for testing—notably, to ensure the proper pressure drop between points of interest.
Alternatively, pressure vacuum breakers (PVB) developed as a result of a need for an atmospheric inlet valve that could be utilized under constant pressure and that could be tested inline. The (PVB) includes a spring that sits on top of a disc or float assembly with two shut-off valves and a series of test cocks. (PVB) assemblies also include a single check valve. When pressure decreases to a pre-set point, the air inlet valve opens. One drawback of the (PVB) assemblies is that they are not designed to protect against backpressure conditions. As a result, the installation must be a minimum of 12 inches higher than all downstream usages.
The spill resistant pressure vacuum breaker (SVB) is essentially a modification to the (PVB) assembly, wherein the (SVB) is designed to minimize water spillage. Installation and backpressure requirements of the (PVB) and (SVB) are similar to one another and both devices are recommended for limited usage.
All of the check valves on all of the backflow assemblies are designed to close in the event of a significant pressure drop or pressure reversal in the supply line. In this respect, a spring loaded check valve has a predetermined tension that requires a certain amount of flow to be exerted thereon to remain open. If certain flow conditions exist within the piping system (e.g., low flow or reverse flow), the spring overcomes the flow in the piping system and the check valve closes. In a closed condition, water is not allowed to flow backward from the outlet toward the distribution center. Additionally, a relief valve or float valve opened to the atmosphere may be activated under other conditions in the event pressure in the system drops to a present opening point, to introduce air into the system to prevent back-siphoning conditions or unsafe operating conditions. A leaking check valve or stuck relief/vent valve, may fail to open in the event of a pressure drop or pressure reversal causing unsafe operating conditions. Check valves and relief/vent valves must be periodically tested to ensure that they are in adequate operating condition. Faulty check or relief, vent valves of this nature present the same problems identified above with a system that does not include a means to prevent backflow.
All backflow assemblies are designed to have very low pressure loss when installed on distribution systems, so check valves will only have one to five PSI pound spring loads.
All backflow prevention assemblies are designed to product performance standards and once a year they must be tested using pressure gauges to determine if the assemblies are still performing to the standards in which they were designed.
All backflow prevention assemblies are tested in descending pressure readings, and never in ascending readings as in their product design. Pressure gauges were initially used to test the operability of the backflow assembly as a means for indicating if there is a check valve leakage within the backflow assembly. Of course, pressure gauges have a variety of pressure range capacities and reading accuracies. Normally, a pressure gauge should be selected based on the desired minimum resolution (i.e., the lowest readable pressure range increment). For example, a gauge that can record readings upwards of 500 PSI will not be able to read increments to the same accuracy as a lower pressure 15 PSI gauge if you are only interested in readings in low pressure ranges (i.e., 15 to zero PSI). The minimum increment of the 500 PSI gauge may be as low as 10 PSI while the minimum increment of the 15 PSI gauge can be as low as a half of a tenth PSI (i.e., 0.05 PSI). All backflow preventers are tested in the pressure range of 15 PSI to zero PSI even though they may be located on systems that have pressures over two hundred pounds. When testing a check valve on a backflow assembly, the only interest is whether it holds drip tight above one PSI (1.0 PSI). At one PSI, there is no possibility of a backflow condition.
There are many instances when a gauge is used for testing water or liquid distribution systems where the line pressure may not be known before the gauge is installed. A gauge installed on a distribution system having a line pressure that far exceeds the maximum PSI rating of the gauge, will more than likely destroy the gauge. At a minimum, it can be expected that the accuracy of the gauge will be significantly adversely affected. This is a common problem, for example, when there is a need to test the function of a valve coupled to a water system that has a high input water pressure (e.g., around 200 PSI), but there is a need to check if the valve closes drip tight by measuring pressures under 15 PSI (e.g., in the 1-2 PSI range at 0.05 to 0.1 PSI increments).
So, until now, there has been no equipment for attaching a low pressure gauge to a high pressure system without damaging the low pressure gauge. As a result, differential pressure gauges became the gauge of choice because of their capability of measuring differential pressures to 1 or 2 tenths PSI in a high pressure water system. In this respect, it would be possible to measure the pressure drop across one or more check valves integrated as part of a backflow prevention device in a high pressure line. In fact, some differential pressure gauges are designed to read pressures in the 0-15 P.S.I.D. range and can be connected to a water system that has pressures above 200 PSI, all without destroying the gauge. Despite being frequently used to perform testing of check valve operability, differential pressure gauges do have several major drawbacks, especially when used incorrectly. Differential pressure gauges are designed to read differential pressures and not line pressures. When a differential pressure gauge is attached to a pressure system pressurizing only the high side, the gauge may be damaged such that the gauge may no longer be able to read pressure differentials to the requisite resolution and accuracy.
As a result, the four types of backflow prevention devices mentioned above require an elaborate process for testing check valves. This is due, in part, to the flow through design of the differential pressure gauge, which comes in two valve, three valve, and five valve configurations. For example, U.S. Pat. No. 5,566,704 to Ackroyd discloses a method for using a differential pressure gauge to test the performance of the check valves in a backflow preventer. But, this process is complex and requires bleeding all of the air out of each test cock on the backflow preventer. In fact, all differential pressure gauges approved for testing backflow prevention devices must have the capability of bleeding all the air out of the test equipment because the gauge must be capable of performing the test under hydraulic conditions. The differential pressure gauge must be able to read pressure differentials as low as one tenth (0.1) to two tenths (0.2) PSI on the test equipment scale plate. The check valve of a backflow prevention device must hold one pound of pressure in either direction of flow. A check valve that reads one (1.0) PSI or higher is reported on a test form as holding tight. But, if the check valve gives the tester a reading of 0.9 PSI, one tenth of a pound below the one pound minimum requirement, then the check valve is recorded as failed. If the differential pressure gauge goes to zero, then the check valve is recorded as leaking.
The Cross-Connection Control Manual endeavors to standardize the testing procedure for backflow preventers. The variety of valves, quantity of hoses on models of testing equipment, and a variety of other factors cause confusion and interject errors into the testing process that can lead to inaccurate and/or inconsistent testing results. The industry started testing backflow preventers using only the high side of a 0-15 PSI rated differential pressure gauge not realizing that the gauge accuracy is affected by this simplified testing method. Over time, the spring in the differential pressure gauge wears and loses tension. Most rubber diaphragm differential pressure gauges have a span adjustment screw located on the low pressure side where the spring is located. Tightening the screw replaces the lost tension in the spring. Accordingly, adjusting the screw allows the gauge to be calibrated back to zero when no pressure is present. On one hand, this helps ensure the accuracy of the testing equipment. Although, on the other hand, unless the differential pressure gauge is checked before use, measurements may read high in the event the calibrated adjustment is not made prior to conducting the test. If the differential pressure gauge is used only for pressurizing the high side, then spring tension memory loss is accelerated.
It is typically not recommended to use the differential pressure gauge in the manner described above because of the over-ranging that is taking place with respect to the spring. In fact, the spring can start losing memory immediately after calibration. Additionally, high line pressure and water hammer are two of the most common issues that affect gauge accuracy. In view that one tenth (0.1) PSI has been established as the minimum pressure change increment for determining whether a check valve passes or fails a test, having a gauge that is susceptible to immediate memory loss (resulting in high readings) undoubtedly makes it nearly impossible to use these gauges to accurately test the proper operation of the backflow prevention device.
As such, the state of the art is devoid of prior art that is able to incorporate a low pressure gauge having a minimum PSI rating far below the line pressure, that is capable of measuring relatively small pressure increments. One prior art reference, for example, U.S. Pat. No. 6,705,173 to Elberson discloses an air flow rate meter capable of measuring relative pressure changes with a low-pressure gauge (rated at 0-3 PSI) connected in-line in a high pressure system (e.g., 100-130 PSI). The Elberson pressure gauge is designed to monitor the flow of air in a high-pressure compressed air system. The low pressure gauge is contained within a sealed, high pressure body connected to the high-pressure compressed air line. The low pressure gauge pneumatically connects to opposite ends of a tube disposed within the meter through which the main air pressure line flows. The gauge measures a pressure drop across a restricted orifice defined by the tube. Importantly, the air flow rate meter design protects the low-pressure gauge from being exposed to pressures that exceed the rating of the gauge—pressures that may otherwise damage or permanently destroy the low-pressure gauge.
But, the Elberson air flow rate meter can only be used with air or gas, and not hydraulic fluids. More specifically, the Elberson air flow rate meter is not designed to measure static pressure in a system (e.g., above ten PSI) or the pressure gauge will be severely damaged. Rather, the rate meter is designed only to measure the pressure drop across a particular point of air flowing by a certain throttle. As such, Elberson is an air flow monitor and not a pressure limiting valve that can be utilized with several thousand pounds of pressure. In essence, the Elberson monitor only works if there is a continuous flow through a constricted venturi passage, which creates a differential pressure. The Elberson device cannot work in a static environment, such as in the testing of backflow prevention devices, because there is no continuous flow.
In fact, several other prior art references that disclose high and low pressure gauges do not operate in a static environment. For example, U.S. Pat. No. 3,270,557 to McClocklin discloses a hydraulic circuit tester having a low pressure gauge and a high pressure gauge, but the pressure gauges are not designed to measure static pressure. Specifically, McClocklin discloses a main flow passage having a flow meter disposed therein that measures the flow rate of liquid flowing through the hydraulic circuit tester. A secondary passage diverts liquid from the main passage to a transversely extending passage having a high pressure branch and a low pressure branch connected to high and low pressure gauges, respectively. The low pressure branch includes a valve closure member biased in an open position by a spring and is disposed upstream of the low pressure gauge. When the pressure flowing through the McClocklin device is less than the maximum pressure of the low pressure gauge, liquid flows around the valve closure member, through a slot, and into the low pressure gauge. The liquid delivered to the low pressure gauge then flows into a recess behind the valve closure member and through a series of passageways back to the main flow passage, where the water exits the unit. If the pressure in the device exceeds the rating of the low pressure gauge, the valve member closes, thereby blocking liquid flow to the low pressure gauge. In this respect, the McClocklin device measures dynamic pressure, not static pressure, because liquid flows through device while the pressure is measured.
GB Patent No. 1,502,124 to Collins discloses a pressure regulator that reduces the pressure of gas delivered to an oxygen mask or welding torch from a relatively higher pressure source, but does not measure static pressure. More specifically, the Collins device includes a high pressure chamber that receives high pressure gas from the source and a low pressure chamber that delivers low pressure gas to the welding torch or oxygen mask. A valve stem actuated by a string-supported diaphragm moves relative to a valve seat to control the pressure of the gas delivered to the low pressure chamber. The diaphragm moves the valve stem closer to the valve seat to reduce the pressure of the gas in the low pressure chamber if the pressure in the low pressure chamber is too high. Conversely, the diaphragm moves the valve stem away from the valve seat to increase the pressure of the gas flowing into the low pressure chamber if the pressure in the low pressure chamber becomes too low. Collins also discloses high and low pressure gauges that measure the pressures in the high and low pressure chambers, respectively. Importantly, however, Collins measures dynamic pressure with the high and low pressure gauges in the high and low pressure chambers, respectively, as gas flows through the Collins device; and not as static pressure.
The prior art also includes several devices that seek to control the flow rate or pressure of a fluid. But, in addition to not measuring the fluid pressure therein, these devices control dynamic fluids, not static fluids. For example, U.S. Pat. No. 3,886,968 to Murrell discloses a flow control device that provides a substantially constant flow in the presence of varying inlet pressures and downstream load conditions. More specifically, Murrell discloses a diaphragm dividing a circular casing into upper and lower chambers. A coil spring is disposed between the casing and the diaphragm in the upper chamber. The casing includes an inlet that provides fluid to both the upper and lower chambers and an outlet that allows fluid to exit the upper chamber. The diaphragm includes a valve member integrally disposed thereon that moves relative to a valve seat on the outlet as the diaphragm moves up and down in response to pressure differentials between the upper and lower chambers. As such, the proximity of the valve member to the valve seat determines the volume of fluid flowing through the device. Consequently, Murrell controls the flow rate of a dynamic fluid; and does not measure the pressure of a static liquid.
U.S. Pat. No. 4,733,919 to Jacobs discloses an integrated pneumatic pressure exhaust valve and fluid coupling for tractor trailer air brake systems. But, this device is only operable with dynamic gases (e.g., air that actuates brakes). More specifically, Jacobs discloses a hollow body having an inlet port, an exhaust opening generally coaxial with the inlet port, and an outlet port disposed at a generally right angle relative to the inlet port and the exhaust opening. The inlet port includes a membrane having multiple apertures therein and the exhaust opening includes a frusto-conical plug also having multiple apertures therein. A flexible diaphragm is positioned between the plug and the membrane such that the diaphragm blocks any air from flowing through the apertures in both the membrane and plug when no air pressure is applied to the brakes. When the driver applies the air brakes, the pressure in the inlet port forces the diaphragm against the plug. The outer edges of the diaphragm deflect against the angled sides of the frusto-conical plug, thereby allowing air to flow from the inlet port through the apertures in the membrane and into the outlet port for eventual delivery to the brakes. When the driver releases the brakes, the pressure on the inlet side of the diaphragm becomes significantly lower than the pressure on outlet side thereof. In this respect, the diaphragm deflects forwardly against the membrane and blocks the apertures therein. This deflection opens a flow path between the outlet port and the exhaust opening, thereby allowing the high pressure air in the outlet port to vent into the atmosphere via the apertures in the plug. In this respect, the Jacobs device controls the flow of a dynamic gas and does not otherwise measure the pressure of a static liquid.
Thus, there exists a significant need for a pressure limiting valve usable for testing a pressure drop across a check or relief valve incorporated into a backflow preventer, a pressure drop that is relatively significantly lower than the line pressure along which the backflow preventer serves. Such a pressure limiting valve preferably includes a single inlet pressure limiting valve having means for protecting a low pressure gauge attached thereto for measuring the pressure drop. The valve includes an upper and a lower chamber generally separated by a flexible rubber diaphragm, yet fluidly coupled by a conduit, a spring actuable via movement of the flexible diaphragm in response to pressure changes in the valve body to generally bias a closure seat in an open position relative to the outlet when the valve body is not under pressure and facilitate compression to permit the closure seat to seal the outlet when pressure in the valve body approximately reaches a maximum PSI rating of the low pressure gauge. The present invention fulfills these needs and provides further related advantages.